Explosive



Patented Feb. 1, 1938 I UNITED STATES PATENT OFFICE arouse EXPLOSIVE Harold A. Lewis, Wilmington, Del, and Fred R. Wilson, Bloomfield, N. 3., assignors to E. ll. du Pont de Nemours & Company, Wilmington,

, lDeL, a corporation of Delaware No Drawing. Application January 22, 19 Serial No. 60,260

8 (Claims. (Cl. 52-14) This invention relates to a new and improved the time of maximum hot pressure development detonating explosive and more particularly to one have not been standardized, and in the case of adapted for use in coal'mining where the prodetonating explosives in particular, no reliable duction of coal in the form of large lumps is procedure is known whereby reproducible results desirable. may be obtained. Indeed, the data obtained by The blasting impulse which is imparted by'the the known methods are of such doubtful value explosive to its environment is, in part, a function as to be lacking in significance. For these reaof the reaction rates of two closely related consons, the performance of the explosive in actual secutive chemical reactions, namely: (1) the rate blasting is a more reliable, indication of the ill of initiation of the explosive decomposition; and rate of pressure development than the results of 10 (2) the rate at which the explosive decomposition comparative tests in a Bichel bomb, for example. takes place after initiation. Based on the wide One of the most accurate of these field tests differences in the reaction rates of various explois a statistical study of the amount and size of sives, it is customary to classify them into (a) defthe lumps produced in the shooting of coal with lagrating explosives, in which the two rates menthe powder under evaluation. With typical clefl tioned above are relatively slow; and (b) detonaflagrating explosives, such as black powder for ing explosives, in which the two rates are generalexample, large amounts of lump coal will be proly extremely rapid. duced, since the characteristically low velocity of The first of the two factors mentioned above the propagation and low rate of pressure developmay be expressed in slightly difierent terms as the ment will produce a heaving rather than a shatrate of propagation, or the rate at which the initering effect on the material blasted down. With tiating impulse travels down a column of explodetonating explosives on the other hand, a greatsive. In the case of defiagrating explosives, the er proportion of pulverized material or fines initiating impulse is a flame which travels down will be produced depending on the magnitude of a column of black powder, for example, at a rate the two rates mentioned above. of about 300 m./sec. For detonating explosives From the foregoing, it will be seen that deflaon the other hand, the initiating impulse is a grating explosives such as black powder are- Shock Such as & detonation Wave, which p ,more satisfactory in coal shooting, from the point coeds down a column o dynamite, for p a. of view of execution, than the detonating ex- 39 at a V ty generally in excess Of 1700 -/Se plosives heretofore available, due to the greater The r of propagation f an explosion av is economic value of lump coal. Black powder has readily r d by a y accurate m th s a characteristic disadvantage, however, of prowhioh generally oonsistlin asu i th time r ducing a flame of considerable length and duraqu f r a pl s wav o pass m one tion, which makes this explosive out of the quesbeing tested, for example in the case of detonatmable ases are present.

ing explosives, by means of the well known Mette- For the reasons given above, coal mining 0pa Recorder t e Dautriche methoderations frequently require a detonating explo- Tho Second factor in the blasting impulse, sive which may be safely used in fiery mines. For

p int to another along a col o the explosive tion for safety reasons in mines where infiam- 4o namely, the rate at which the chemical dooome such purposes the most approxed explosives are po i n t s place at a given point alter t the so-called permissible explosives which are initiating impulse has reached that po nt and designated as Such by the Bureau f m Started the deFompositloni is a true reactlon a after passing certain prescribed and ofiicial tests. and as such, is extremely dimcult to determme The great majority of the Smwned permissb wlth some mdlcation of the magmbles contain ammonium nitrate as the principal tude of this rate may be obtained by observing the ingredient These ammonium nitrate permissipliefisure changes in au-closed System and deter bles generally comprise, for example, to 80% mining the so-called rate of pressure developa onium nitrate 10 to 157 nitroglycerme as ment. Since this is a rapidly changing differeni nt u 10 and as hi h as 50 tial function, it is the common practice to deterg Sens 12mg ngre e g {bl t 1 d mine the so-called time of pressure develop- 0% of ca'rbonaPfaous com us 1 8 an ment, or the time required for the explosive to frequently addltwns Safety mgledlents' cooling salts such as sodium nitrate, ammonium develop the maximum hot gas pressure, when suitably initiated. chloride, sodium chloride, ammonium oxalate and The methods of measuring either the rate or the l ke in va y p a Thus, for e ample, in the case of sodium nitrate, the most commonly used safety ingredient, the percentage varies from about 3 to 10%.

Typical examples of ammonia permissibles according to the prior art are shown in Table I.

Table I A B C D Nitroglycerine l0. 0 11. 0 1i. 0 14. 0 Ammonium nitrate 75. 0 78. 5 75. 0 65. 5 Safety ingredients 5. 5 3. 0 4. 0 3. 0 carbonaceous combustibles 9. 2 7. 2 9. 7 17. 2 Antucid 0.3 0.3 0. 3 0.3

Velocity, m./sec. 2750 2200 1900 1850 Density 1. 0 1. 0 0. s 0.65 Nitroglycerinegrams per 100 cc. explosive 10.0 11.0 8. 8 9. 1

From the safety standpoint, such permissible detonating explosives have given great satisfaction and they have been excellently adapted for use with many types of coal from the viewpoint of execution. In cases, however, where the coal is soft and offers little resistance, and where a high percentage of lump coal is desired, such explosives are too violent in their action to give the desired results. This violence of action, as above explained, is due in part to the velocity of propagation, but by far the more important factor is believed to be the rate of pressure development. Since, however, the rate of pressure development can only be inferred indirectly from the performance of the explosive in actual use in the field, the exact explanation of the failure of prior permissibles to give the desired results under these circumstances is not definitely known, but the explanation given above appears to be correct.

The object of the present invention is an improved detonating explosive adapted for use in coal mining and producing a relatively large percentage of lump coal. A further object is such an explosive characterized by high strength, but having at the same time a low rate of pressure development. A still further object is a detonating explosive having a very low velocity and a very low rate of pressure development. Additional objects will be disclosed as the invention is hereinafter more fully described.

We have found that the foregoing objects are accomplished by introducing into the explosive composition ammonium nitrate in an amount at least equal to 65% and preferably 75 to said ammonium nitrate being so controlled as to grain size and so sensitized with nitroglycerine or other nitric esters as to make certain a velocity less than 1700 meters per second and a low rate of pressure development. The ammonium nitrate used is of such a degree of coarseness that substantially the greater part thereof (i. e. over is held on a 35-mesh screen, and preferably we find it desirable to use even coarser grains, such for example that substantially the greater proportion thereof (i. e. over 80%) is held on a 24-mesh screen. The sensitizer used, nitroglycerine or other explosive nitric esters, is used in an amount not exceeding 7.5 grams per cc. of explosive, and preferably between 4.5 and 6.5 grams per 100 cc. of explosive.

As illustrative of the preferred ranges within which the variousingredients of our explosive may be used, reference is made to Table II.

In the foregoing table the ammonium nitrate employed is of a degree of coarseness such that substantially the greater part thereof (e. g., over 80%) passes a IO-mesh screen but is held on a zi-mesh screen.

In explosive compositions of the type shown in Table II there is a minimum amount of sensitizer which is necessary for detonation; this is usually 3.0 to 4.0 grams of sensitizer per 100 cc. of explosive. In practice, it is necessary to use an amount slightly above the minimum in order to obtain a practical explosive composition. On the other hand, if an amount of sensitizer is used that is too far above the necessary minimum, then the reactions are set up with such violence that the rate of pressure development is increased and thus adversely affected for the purposes of our invention. The compositions shown in Table II therefore all contain an amount of sensitizer less than 7.5 grams per 100 cc. and within the preferred range of 4.5 to 6.5 grams per 100 cc.

The safety ingredients preferably comprise sodium nitrate, but any other of the well known cooling salts may be used if desired. The carbonaceous combustibles may consist of oat hulls, corn meal, bran, ground coal, wood pulp, expanded cereal products, cottonseed hulls, rice hulls, ivory nut meal, starch, flour and the like, or any mixtures thereof. Preferably, however, we use those combustibles which give compositions of a high degree of sensitiveness, particularly in those compositions of low density. As an example of this type of combustible, we may mention flaked cereal products such as flaked corn, wheat, rye, starch, hominy grits and the like. The antacid may consist of calcium carbonate, magnesium carbonate, magnesium oxide and the like.

As specific examples of a permissible type explosive in accordance with our invention, we may cite the compositions illustrated in Table III.

A typical screen analysis of the ammonium nitrate employed in the examples given in Table III is indicated in Table IV.

Table IV Held on 10 mesh Held on 10-14 mesh Held on 14-20 mesh Held on 20-24 mesh Held on 24-28 mesh Held on 28-35 mesh Held on 3565 mesh Pei-cent Held on 65100 mesh Passing 100 mesh S coi-waowswusw nitrate could be successfully detonated at full' strength ,with as little as 4 to 7% nitroglycerine.

In particle size, the relatively coarse ammonium nitrate heretofore employed was such that at least 80% was held on a GO-mesh screen, and not more than 20% passed therethrough. Our

. invention, however, contemplate-s the use of much coarser ammonium nitrate, for example such that at least 80% is held on a 2 i-mesh screen.

At first glance, this may appear to be an inconsequential difference from the ammonium nitrate heretofore employed, for example by Woodbury and Ward. This increase in the particle size, however, produces the surprising result that the powders according to our invention have a much lower rate of pressure development, and therefore produce an appreciably higher percentage of lump coal. Heretofore no one appears to have recognized that the rate of pressure development of ammonia dynamites may be lowered by employing ammonium nitrate of very large particle sizes as above described. By actual tests, however, we have found this to be the case. This is clearly indicated in Table V.

Table V Percent coal held on 2-inch Explosive used mesh Table V gives the results of a statistical study of the percentage of fines produced by various permissibles when used to pull coal in the same mine under comparable blasting conditions. In this table the results obtained by the use of the composition A of Table III according to our invention are compared to those obtained with the prior art compositions A and B of Table I. It will be noted that whereas there was an increase of 4% of 2-inch lump coal obtained by the use of composition B of Table I having a velocity of 2200 meters as compared with composition A of Table I having a velocity of 2750 meters, there was an increase of 2-inch lump of from 36 to 44% when employing composition A of Table III in accordance with our invention. This increase of from 36 to 44% represents an actual increase of 22% in the lump coal produced.

As mentioned above, the velocities of compositions A, B and C in Table III are somewhat lower than the corresponding properties of the common prior art permissibles. By far the more important change, however, resulting from the selection of grain sizes is an unexpected and very appreciable reduction in the rate of pressure'development of the explosive, as indicated by actual tests in the field, for example, as shown in Table V. An explosive such as those described in Table III will possess to an unexpected degree the prop-- erties necessary for producing lump coal and will have high strength, between 50% and 60% straight dynamite, due to its high content of explosive material, namely, nitroglycerine and ammonium nitrate. The strength, however, will develop slowly because of the presence of ammonium nitrate in the form of. very coarse grains. The low nitroglycerine content will be insufiicient to cause the rapid development of pressure from the coarse grains of ammonium nitrate, but will be ample to develop the maximum strength of the explosive when the latter is shot in cartridges of sufficiently large diameter.

An explosive such as the foregoing is not consistently capable of detonation at its full explosive strength when shot in the smaller diameters usual in prior art coal blasting. It has been the custom, for example, to consider cart-ridges of 1 diameter as a standard. Our explosive, however, cannot effectively be used in diameters appreciably lower than 1 since the danger of misfires is too great. Consequently, the utilization-of explosives according to our invention in diameters not less than 1 is a prerequisite, and preferably the cartridge should have a diameter of 1%" or more.

It will be apparent to any one skilled in the art that a notable advance has been made possible by our new explosive. The superior qualities of black powder in the breaking down of coal in the form of large lumps has long been recognized. To the best of our knowledge, however, the present invention is the first to recognize that detonating explosives of the dynamite type, containing very lar e particles of ammonium nitrate, are capable of producing similar favorable results. Thus, by the use or" our explosives, it is possible to produce a significantly higher percentage of lump coal in the presence of fi e-damp than has ever been achieved before with a permissible ammonium nitrate dynamite.

In the foregoing detailed description or" our invention, it is apparent that many changes and modifications may be introduced Without departing from the spirit and scope thereof. For example, the term nitroglycerine as employed in this specification and the appended claims is used in the sense in which it is employed in the art. i. e. it includes not only nitroglycerine as. such, but the various explosive nitric esters commonly used in place of, or in mixtures with, nitroglyccrime, for example ethyleneglycol dinitrate, tetranitrodiglycerine, nitrated sugars, nitrostarch, nitrochlorhydrins, pentaerythritol tetr'anitrate and various mixtures of these and similar substances. In addition, aromatic nitrocompounds such as the dinitrotoluenes, the nitroxylenes, and the like, and similar explosive materials may be added if desired. Furthermore, the liquid nitric esters may be slightly gelatinized if desired by the addition of small percentages of nitrocotton or other gelatinizing agents. Other variations will be an parent toanyone skilled in the art. We, therefore, intend to be limited only in accordance with the following patent claims:

We claim:

1. An ammonium nitrate explosive charge adapted for use in coal mining, and having a low velocity and a low rate of pressure development, said explosive comprising more than ammonium nitrate of a degree of fineness such that substantially the greater part thereof will be held on a 24-mesh screen and substantially all thereof will be held on a 35-mesh screen, said explosive being cartridged in a diameter not less than 1 whereby a substantially complete utilization of the explosive strength of the ammonium nitrate is assured.

2. An ammonium nitrate explosive charge adapted for use in coal mining, and having a low velocity and a low rate of pressure development, said explosive comprising at least 65% ammonium nitrate of 'a degree of fineness such that substantially all thereof will be held on a 35-mesh screen, and a sensitizing agent comprising not more than 7.5 grams explosive nitric ester per 100 cc. of explosive, said explosive being cartridged in a diameter not less than 1 whereby a substantially complete utilization of the explosive strength of the ammonium nitrate is assured.

3. An ammonium nitrate explosive charge adapted for use in coal mining, and having a low velocity and a low rate of pressure development, said explosive comprising not more than 7.5 grams of nitroglycerine per 100 cc. of explosive, and at least ammonium nitrate of a degree of fineness such that substantially all thereof will be held on a 35-mesh screen, said explosive being cartridged in a diameter not less than 1 whereby a substantially complete utilization of the explosive strength of the ammonium nitrate is assured.

4. An ammonium nitrate explosive charge adapted for use in coal mining, and having a low aroma? velocity and a low rate of pressure development, said explosive comprising 4.5 to 6.5 grams of nitroglycerine per 100 cc. of explosive and at least 75% ammonium nitrate of a degree of fineness such that substantially all thereof will be held on a 35-mesh screen, said explosive being packaged in a diameter not less than 1 inches.

5. An ammonium nitrate explosive charge adapted for use in coal mining, and having a low rate of pressure development, said explosive comprising 4.5 to 6.5 grams of nitroglycerine per 100 cc. of explosive and from '75 to ammonium nitrate of a degree of fineness such that substantially all thereof will be held on a 35-mesh screen, said explosive being packaged in a diameter not less than 1 and having a velocity lower than 1700 m./sec.

6. A high strength ammonium nitrate permissible-type explosive charge adapted for use in coal mining, and having a low rate of pressure development, comprising approximately 4.5 to 6.5 grams nitroglycerine per cc. of explosive, 75 to 85% ammonium nitrate of a degree of fineness such that substantially the greater part thereof will be held on a 24-mesh screen and substantially all thereof will be held on a 35-rnesh screen, 1 to 5% of sodium nitrate, 5.0 to 15% of a carbonaceous combustible which favors sensitiveness at low percentages of nitroglycerine, and 0.5% chalk, said explosive having a velocity lower than 1700 m./sec. and being cartridged in a diameter not less than l 'flwhereby a substantially complete utilization of the explosive strength of the ammonium nitrate is assured.

'7. The composition of claim 6, in which said carbonaceous combustible comprises a flaked cereal product.

8. The composition of claim 6, in which said carbonaceous combustible comprises a flaked corn product.

HAROLD A. LEWIS. FRED R. WILSON. 

